Reciprocating floor conveyors have been used for several years in van bodies and in trailers for unloading cargo. These conveyor systems are widely used for transporting bulk material such as ground plant material for animal feed, saw dust, wood chips, bark and plant material for human consumption. The conveyor systems include a plurality of parallel floor slats each of which extends substantially the length of the van body or trailer on which it is mounted. Each floor slat is supported by two slide bearings that permit it to slide back and forth in a direction parallel to its long axis.
Several different drives and drive systems have been employed in reciprocating floor conveyors to reciprocate the floor slats back and forth. A commonly used drive system includes three hydraulic cylinders that move all the slats simultaneously to the rear toward a rear discharge charge carrying cargo with them. The first cylinder is connected to and drives every third floor slat. The second cylinder is connected to and drives all the floor slats that are adjacent to a common side of the floor slats attached to the first cylinder. A third cylinder is connected to and drives the floor slats that are each between a floor slat driven by the first cylinder and a floor slat driven by the second cylinder. The first, second and third cylinders are activated one at a time to move every third floor slat forward and away from the rear discharge without moving cargo forward. The floor slats do not convey cargo when two thirds of the floor slats are stationary while one cylinder moves one third of the slats forward. The third cylinder moves the floor slats connected to it forward while the floor slats connected to the first and second cylinders remain stationary. The second cylinder then moves the floor slats connected to it forward while the floor slats connected to the first and third cylinders remain stationary. The first cylinder then moves the floor slats connected to the first cylinder forward while the floor slats connected to the second and third cylinders remain stationary. The above procedure is then repeated to move the cargo through the rear discharge opening. The procedure continues to be repeated until all the cargo is discharged.
Floor slats are commonly made form aluminum or other suitable material. Space is provided between aluminum floor slats to accommodate thermal expansion of the floor slats and to prevent galling. Galling can occur when aluminum floor slats are moving relative to each other and in contact with each other. The gaps between adjacent floor slats in reciprocating floor conveyors create two problems. One problem is the loss of cargo. This is not a serious problem if the cargo is non-toxic and inexpensive. Loss of cargo is a serious problem, however, if the cargo is a toxic material or if the cargo is expensive. The second problem is cargo contamination. Cargo can be contaminated by water and other material on a road surface that is thrown outwardly by vehicle wheels and passes through spaces between the floor slats. Cargo contamination is an extremely serious problem if the cargo is for human or animal consumption.
Two basic types of solutions to the problem caused by the space between floor slats have been tried. One solution is to place a fixed sub-floor under the floor slats to catch the material that passes between the floor slats and to prevent outside contaminates from contacting the floor slats. This solution adds weight and expense to reciprocating floor conveyor systems. Catching material that passes down between the slats also adds disposal problems if it is necessary to dispose of the material that is caught. Seals between the floor slats have been the preferred solution to the problem. Seals between the floor slats can virtually eliminate cargo loss as well as cargo contamination. Seals between reciprocating floor slats are generally resilient and rely upon their resilience to maintain sealing contact. Seals that can be inflated have also been tried. Inflated seals are deflated during conveying operations.
Some seals that are currently in use are carried by one floor slat and are in sliding contact with a vertical or near vertical surface on the side of the adjacent floor slat. These seals are made from the materials that have a low coefficient of friction, that are tough, and that are resilient. The low coefficient of friction is required to minimize the force required to reciprocate the floor slats back and forth and to prolong seal life. The seals must be made of tough material to prolong seal life and to prevent the penetration of cargo. Resiliency is required to accommodate variations and the size of the gap between floor slats and to maintain sealing contact between the seals and sliding contact surfaces on adjacent floor slats.
The floor slats slide fore and aft on bearings that support and guide each floor slat. These bearings allow limited lateral movement of the floor slat. Cargo may therefore move the floor slats laterally. If the reciprocating floor is slightly lower on one side than on the other side, the cargo will tend to move the floor slats toward the low side. This results in a decrease in a gap between some floor slats and an increase in the gap between other floor slats. The seals that slide on a vertical or near vertical surface must have the ability to accommodate the changes in the gap between adjacent floor slats. Seals that have been used in the past can accommodate only small changes in the size of the gap between adjacent floor slats.
Some seals that are currently in use are compressed when the gap between adjacent floor slats decrease. With a few seal designs a portion of the seal can become pinched between the surfaces on adjacent floor slats. This pinching increases the load between the seals and the floor slat surface. The increased load due to seal compression or due to pinching the seal increases the power required to reciprocate the floor slats and increases wear.
Cold temperatures tend to stiffen resilient seals. It has been found that some seals that are stiffened by low temperature can wear through the side of a floor slat thereby destroying the floor slat in a relatively short period of time.
Abrasive cargo increases the wear between floor slats and seals that are in sliding contact with each other. Some parts of floor slats cannot accommodate much wear without the floor slat being essentially destroyed.
Some floor slat seal designs, that are currently in use, create a pocket which catches and retains solids and liquids that pass through the space between the upper portions of adjacent floor slats. In cold weather the liquid and solids freeze. The frozen liquids and solids may exert large forces on seals due to the expansion of the liquid as it turns to ice. The excess force on the seals increases the force required to reciprocate the floor slats and increases wear on the seals and seal contact surfaces. The solids held by the frozen liquids also increase wear on the floor slats and the seals if the solids are abrasive.